Broadband measurements of reflection coefficient with the use of Butler matrix

A novel application of a 4 × 4 Butler matrix in a broadband reflectometer is presented. The well-known dedicated multiport has been replaced with a standard 4 × 4 Butler matrix with reflective element connected to the one of its ports. It is shown, that properties of such a network allow for the complex reflection coefficient measurements. In order to broaden measurement frequency range, a simple modification of a calibration procedure is proposed. The presented system has been verified experimentally by the measurement of reflection coefficients of three shorted attenuators in frequency range 1 - 5 GHz. The measurements have been compared with ones obtained with the use of commercial VNA, showing good agreement.